The present invention relates to a chemical mechanical polishing slurry. In particular, it relates to a chemical mechanical polishing slurry suitable as a polishing liquid used during forming a damascene copper interconnect in manufacturing a semiconductor device.
With regard to forming a semiconductor integrated circuit such as ULSI which has been significantly refined and compacted recently, copper has been expected to be a useful material for electric connection because of its good electromigration resistance and lower electrical resistance.
To date a copper interconnect is as follows, due to problems such as difficulty in patterning by dry etching. Specifically, a concave such as a trench and a connection hole is formed in an insulating film, a barrier metal film is formed on the surface, a copper film is deposited by plating such that the concave is filled with the material, and then the surface is polished to be flat by chemical mechanical polishing (hereinafter, referred to as xe2x80x9cCMPxe2x80x9d) until the surface of the insulating film except the concave area is completely exposed, to form electric connections such as a damascene interconnect in which the concave is filled with copper, a via plug and a contact plug.
There will be described a process for forming a damascene copper interconnect with reference to FIG. 1.
On a silicon substrate on which a semiconductor device has been formed (not shown) is formed a lower interconnect layer 1 consisting of an insulating film comprising a lower interconnect (not shown). Then, as shown in FIG. 1(a), on the silicon substrate are sequentially formed a silicon nitride film 2 and a silicon oxide film 3. On the silicon oxide film 3 is formed a concave having an interconnect pattern and reaching the silicon nitride film 2.
Then, as shown in FIG. 1(b), a barrier metal film 4 is formed by sputtering. On the film is formed a copper film 5 over all the surface by plating such that the concave is filled with the material.
As shown in FIG. 1(c), the copper film 5 is polished by CMP to make the substrate surface flat. Polishing by CMP is continued until the metal over the silicon oxide film 3 is completely removed, as shown in FIG. 1(d).
In the above process for forming a damascene copper interconnect, a barrier metal film made of, for example, a tantalum-based metal such as Ta and TaN is formed as a base film for, e.g., preventing diffusion of a copper-based metal into the insulating film. However, when simultaneously polishing such different materials, a polishing rate for the barrier metal film is significantly smaller than that for the copper-based metal film. Specifically, when forming a damascene copper interconnect by CMP using a conventional polishing slurry, there is a significant difference between the polishing rates for the copper-based metal film and the barrier metal film, which may cause dishing and erosion.
Dishing is a phenomenon that the copper-based metal film in the concave is excessively polished so that the center of the copper-based metal film in the concave is depressed in relation to the plane of the insulating film on the substrate, as shown in FIG. 2. More polishing time is required for completely removing the barrier metal film 4 on the insulating film (silicon oxide film 3) because of a lower polishing rate for the barrier metal film. The polishing rate for the copper-based metal film is, however, higher than that for the barrier metal film, so that the copper-based metal film is excessively polished, resulting in dishing.
Erosion is a phenomenon that polishing in a dense interconnect area excessively proceeds in relation to that in a sparse area such as an isolated interconnect area so that the surface of the dense interconnect area becomes depressed in relation to the other surfaces, as shown in FIG. 1(d). When the dense interconnect area comprising many damascenes in the copper film 5 is considerably separated from the isolated interconnect area comprising less damascenes in the copper film 5 by, for example, an area without interconnects within the wafer, and the copper film 5 is polished faster than the barrier metal film 4 or the silicon oxide film 3 (insulating film), then a polishing pad pressure to the barrier metal film 4 or the silicon oxide film 3 in the dense interconnect area becomes higher than that in the isolated interconnect area. As a result, in the CMP process after exposing the barrier metal film 4 (the process of FIG. 1(c) and thereafter), there generates a difference in a polishing rate by CMP between the dense interconnect area and the isolated interconnect area, so that the insulating film in the dense interconnect area is excessively polished, resulting in erosion.
Dishing in the process for forming an electric connection in a semiconductor device as described above, may cause increase in an interconnection resistance and a connection resistance, and tends to cause electromigration, leading to poor reliability in the device. Erosion may adversely affect flatness in the substrate surface, which becomes more prominent in a multilayer structure, causing problems such as increase and dispersion in an interconnect resistance.
It is well-known that benzotriazole or its derivative or 1,2,4-triazole may be added to a polishing slurry for preventing the above problems, in particular dishing formation.
JP-A 8-83780 has disclosed that a polishing slurry comprising benzotriazole or its derivative may be used for preventing dishing during chemical mechanical polishing in forming a damascene interconnect made of copper or a copper alloy. Benzotriazole may act as a protective film preventing oxidation or corrosion in the presence of an etchant having a chemical etching range where copper can be quickly etched. There has been described that a polishing slurry comprising benzotriazole together with an etchant may be used in chemical mechanical polishing so that a reliable conductor film can be quickly formed while preventing dishing or scratches.
JP-A 11-238709 has described that a slurry for chemical mechanical polishing may comprise a triazole derivative such as a 1,2,4-triazole or benzotriazole derivative for improving flatness in copper polishing.
JP-A 8-64594 has disclosed, without describing prevention of dishing, a grain liquid comprising benzotriazole for improving reliability in a semiconductor device by preventing a metal-film interconnect containing copper from being deteriorated due to corrosion during polishing. There has been described that a polishing liquid comprising benzotriazole may be used in polishing to form an anticorrosive film before corrosion so that an interconnect can be reliably formed while preventing corrosion.
As described above, dishing can be inhibited while preventing corrosion, by using a polishing slurry comprising benzotriazole in chemical mechanical polishing. However, as a content of benzotriazole is increased, a polishing rate of copper is reduced, leading to reduction in a throughput. It has been, therefore, difficult to conduct polishing at a higher polishing rate while adequately inhibiting dishing.
An excessive content of benzotriazole tends to cause vibration or vibration noise during polishing a copper film (FIGS. 1(b) to (c)), and in a polishing process where a barrier metal film and/or interlayer insulating film is exposed (FIGS. 1(c) to (d)), an interconnect end may be often damaged from a barrier metal film.
An objective of this invention is to provide a chemical mechanical polishing slurry whereby polishing can be conducted at a higher polishing rate while preventing dishing in chemical mechanical polishing of a copper-based metal film formed on an insulating film comprising a concave on a substrate and to form a reliable damascene electric connection with excellent electric properties.
This invention relates to a chemical mechanical polishing slurry for polishing a copper-based metal film formed on an insulating film comprising a concave on a substrate, comprising a polishing material, an oxidizing agent and water as well as a benzotriazole compound and a triazole compound.
A chemical mechanical polishing slurry of this invention (hereinafter, referred to as a xe2x80x9cpolishing slurryxe2x80x9d) may be suitably used in polishing a copper-based metal (copper or a copper alloy comprising copper as a main component) film formed on an insulating film with a concave on a substrate by CMP.
The slurry may be effectively used in a process for forming a barrier metal film as a base film on an insulating film with a concave; forming a conductive metal film on the barrier metal film such that the concave is filled with the metal film; and polishing by CMP the substrate to flatten the substrate surface until the barrier metal film or the insulating film is exposed so that an electric connection such as a damascene interconnect where the concave is filled with a copper-based metal, a plug and a contact is formed. The slurry is more effective when the barrier metal is a tantalum-based metal.
A polishing slurry of this invention may be used in CMP to form a reliable damascene electric connection with excellent electric properties at a higher polishing rate, i.e., a higher throughput while preventing dishing.